Preparation of Powder Metallurgy Titanium Alloy with Bimodal Structure of High Mechanical Properties

Abstract:

Powder metallurgy (PM) Ti6Al4V alloy with a relative density of 99% was prepared by low temperature vacuum sintering using fine Ti6Al4V powder. To eliminate porosity and control the microstructure morphology, forging was performed. The results show that microstructure of as-forged samples is bimodal structure with long lath primary α and α+β lamellae. The as-forged samples show tensile properties with ultimate tensile strength (UTS) of 1176 MPa, yield strength (YS) of 1100 MPa, elongation (EL) of 18.2%, and good low-cycle fatigue life. The as-forged PM Ti6Al4V has good fatigue performance with more than 10⁵ cycles under the stress of 700 MPa. In order to explore the reasons for good fatigue properties, in-situ observation tests were carried out. It is found that the long lath primary α structure can effectively prevent the crack propagation in the steady propagation stage and prolong the fatigue life. Besides, fully dense structure decreases the fatigue crack initiation. Thus, the bimodal structure shows excellently comprehensive mechanical properties.

Key words:powder metallurgy;Ti6Al4V;bimodal structure;low-cycle fatigue;in-situ observation